1. Field of the Invention
The present invention relates generally to implantable elements for treatment of malignant tumors in the body, and more particularly, to a radioactive filament or core comprised at least partly of substantially pure iridium, and preferably an iridium/platinum alloy, encompassed within a substantially pure platinum sheath, which is adapted to be cut into predetermined sealed lengths without undesirable leakage of radioactivity at the ends of each cut length, for insertion into and shrinkage of body tumors.
2. General Background
In the field of medicine which addresses the treatment of tumors in the body, one such method of treatment, referred to as interstitial brachytherapy, involves insertion into the tumor of implants which have been irradiated to enable them to emit radioactivity, for the purpose of shrinking and ultimately destroying the tumor.
The procedure followed for this type of therapy calls for inserting the radioactive implant through a plastic catheter or similar means previously inserted into the tumor from a point external to the body. The intention is that when the implant is within the tumor, the radioactivity emitted by the implant is sufficient to destroy the cancerous cells in the immediate vicinity. Unfortunately, however, problems exist in using implants of the type presently available on the market. A very common type is the IR-192 isotope in the form of iridium/platinum seeds spaced within a nylon or plastic tube for insertion into the cancerous growth. Typically, the IR-192 seeds are three millimeters (mm) in length and spaced seven mm apart in a configuration which provides a known standard distance of one centimeter (cm) between the centers of adjacent seeds. The IR-192 isotope of the seeds should not be exposed at the exterior surfaces because radioactivity bleeding therefrom could cause serious injury to the adjacent tissue. It is essential, therefore, that the iridium/platinum core be housed in a sheath of platinum at all times. The spacing between seeds in the nylon or plastic tubing which is inserted in the body tumor results in only partial treatment of the tumor because of the lack of uniform emission of radioactivity from the tubing.
Similarly, there are instances in which the tubing containing the IR-192 seeds must be inserted along a path of the body which is not straight, such as would be the case in use of an endobronchial implant, tongue implant, tonsil implant or other implant intended to reach a region of the body not readily accessible for purposes of the treatment. In these instances, it is essential to install a catheter through which the implant tube may be guided as it is inserted to the site of the tumor within the body. The catheter produces a tortuous path or must be installed along such a path, consisting of many turns, tight angles and curves to provide a passage to the location within the body requiring treatment. The IR-192 implant typically must be threaded through such a path, and, because of spacing of the seeds within the tubing of the implant, the traversal of the implant may produce bending or kinking of the catheter or of the tubing of the implant itself, to effectively prevent further movement of the implant and thereby, preclude it from reaching the desired treatment site.
Another prior art type of radioactive implant is marketed in the form of encapsulated IR-192 wires of predetermined length. This implant type is advantageous compared to the seed type described above, because it provides a continuous surface for relatively uniform emission in contrast to the gaps encountered between radioactive portions of the seed type. However, the continuous surface type suffers the limitation that it must be marketed in prefabricated pieces of pre-cut lengths which may be too short or too long for the tumor under treatment. The prefabricated implant cannot readily be trimmed or cut to a desired length at the time it is to be introduced into the patient's body because the cut ends will leak, and damage the surrounding tissue.
Current guidelines for use of radioactive sealed sources such as these implants, require that the source be leak tested at least every six months. The known types of implants meet this guideline since they are carefully sealed at the point of manufacture by complete encapsulation. As noted above, this is not conducive to on-site flexibility of treatment of the various sizes of body tumors requiring treatment. It would be desirable to provide a low dose radioactive implant which is adapted to be trimmed to proper desired length at the point of treatment, rather than fabricated in many different lengths at the point of manufacture and thereby necessitating large inventories of such implants at the treatment facility.
Exemplary of the pertinent prior art are the following U.S. Pat. No. 2,429,438 in the name of Wappler pertaining to tubular bodies such as radium seeds; U.S. Pat. No. 2,322,902, also in the name of Wappler, on apparatus for making such tubular bodies; and U.S. Pat. No. 3,438,365 to Packer et al. on radioactive seed containing xenon gas for medical treatment.